Method and device for storing and transporting flat glass in a contactless manner

ABSTRACT

The invention relates to a method and a device for storing and transporting hot flat glass in a contactless manner during glass production, said storage and transportation being carried out on a gas bed which is constructed over a gas permeable bearing surface pertaining to a base ( 2 ). Pressurised gas is supplied to the base via a connection ( 5 ), said gas being guided through the gas permeable base and then re-evacuated. The aim of the invention is to obtain an optimum pressure distribution above the bearing surface, without any static pressure. In order to achieve this, the base ( 2 ) consists of a plurality of interspaced segments ( 2   1   , 2   2    . . . 2   n ) respectively comprising a porous and/or perforated bearing surface ( 7   a ) as a gas outlet surface. Evacuation openings ( 6   1   , 6   2    . . . 6   n ) are formed between said segments for evacuating the gas. The segments are preferably formed by bars ( 7 ) having a box profile.

[0001] The invention relates to a method for storing and transportinghot flat glass in glass production on a gas bed, which is constructedover a gas-permeable support surface of a nest, in a contactless mannerby passing a gas through the support surface.

[0002] The invention also relates to a device for performing thismethod.

[0003] In the conventional glass ceramicizing process typically used inthe industry, the glass to be ceramicized, typically in the form of aplatelike green glass body, rests on a solid nest. Since during theceramicization process temperatures and viscosities are reached at whichthe glass surface can be harmed by mechanical contact with the nest,punctate prints from adhesion known as “pits” appear on the underside ofthe glass. From a shrinkage process during the ceramicization, arelative motion between the supported glass and the nest also occurs,creating scratches on the glass surface.

[0004] These disadvantages, resulting from the contact of the greenglass plate with the solid nest, lead to the thought of employingprinciples from float glass production. However, in this respect it mustbe noted that the ceramicization process differs from the usual floatglass tempering process in that substantially higher temperatures arerequired, as a rule up to about 950° C., but in special cases even up to1250° C., instead of about 500° C. to 700° C. in the case of temperingand bending furnaces for float glass, and in addition, a temperaturehomogeneity in the range of a few Kelvins must be assured, to preventdeformations of the glass ceramic.

[0005] It is known to ceramicize glass in contactless fashion, byretaining the green glass molded body to be ceramicized on a gas bed inwhich the supporting gas, as a rule air, flows out of a permeable nestand builds up a load-bearing air bed between this nest and the greenglass molded body. Since there is no direct contact between a solid nestand the green glass body, the aforementioned disadvantages cannot arise.

[0006] British Patent Disclosure gas bed 1,383,202 shows a correspondingdevice for contactless ceramicizing of a green glass plate on an airbed. This known device has various disadvantages, however, which resultfrom the fact that work is done solely with a inlet air supply, that is,without outlet air, through the nest, and the inlet air is deliveredthrough perforated plates. With typical perforations, a comparativelyhigh permeability is achieved:

[0007] Calculations show that here in the middle region of the greenglass plate to be ceramicized, the gas speed is nearly zero and as itwere a “static” pressure is generated. A gas flow is created thenessentially only in the vicinity of the edge of the plate. In contrastto the pressure in the edge region, the static pressure in the middle ofthe plate is indifferent to disruptions in the thickness of the gasfilm. Accordingly, no restoring moment resistant to geometric deviationsin the plates from flatness or from the particular desired shape arises.The same situation means that the thickness of the gas film is verysensitively dependent on the magnitude of the pilot pressure and otherprocess parameters. Disruptions in these parameters can therefore causewarping of the plates.

[0008] U.S. Pat. No. 3,607,198 shows a device for contactless retentionand transporting of a hot glass plate on an air cushion that is built upabove a solid nest. Here, in alternation along the transport route, byway of inlet-air and outlet-air slits, zones with static and dynamic gaspressure are created, each extending over the entire width of the glassplate. Since here the gas delivery is effected via narrow slits withlarge interstices between them, the result is a gas supply that islocally very nonhomogeneous, which in turn—because of the alternationbetween zones of high and low gas speed—makes a homogeneous temperaturecourse in the glass difficult. Moreover, a complicated construction isemployed, which for reasons of material is not suitable for use in therange of temperatures around 950° C., and certainly not for highertemperatures of up to about 1250° C., that can be necessary for theceramicization.

[0009] U.S. Pat. No. 5,078,775 also shows a device for contactlessretention and transporting of a flat glass plate, in the tempering offloat glass, on an air cushion that is built up above a solid nest thatlikewise has alternating inlet-air and outlet-air slits. This knowndevice, despite modifications in details, relies on the fundamentalconcept of U.S. Pat. No. 3,607,198, with the inlet-air and outlet-airslits in the nest, and thus with regard to ceramicization applicationshas comparable disadvantages.

[0010] The object of the invention is to conduct the method defined atthe outset for contactless storing and transporting of flat glass, inwhich via a gas bed any contact whatever of the flat glass with the nestis avoided, in such a way, and to embody the associated device in such away, that compared to the known ceramicization methods, flat glassceramic of high smoothness can be produced, and in which thetransporting can be done optionally through a path in the furnace with apredetermined temperature profile. Compared to the known methods anddevices for tempering float glass above an air bed, the object to beattained is that these methods and devices can be employed in astructurally simple way in the temperature range up to 950° C. andhigher, while achieving temperature homogeneity.

[0011] In terms of the method, taking as the point of departure themethod defined at the outset for storing and transporting hot flat glassin a contactless manner in glass production on a gas bed, which isconstructed over a gas-permeable support surface of a nest, in that agas is passed through the support surface, this object is attained inthat to attain a homogeneous delivery of gas sheetwise, the gas ispressed through spaced-apart planar porous and/or perforated segments ofthe support surface, and the gas is carried away into the intersticesbetween the segments.

[0012] In terms of the device, taking the device defined at the outsetfor performing the methods as the point of departure, having agas-permeable nest, disposed in a furnace, as a support surface for theflat glass to be stored and transported in contactless fashion, whichnest has a connection for the delivery of gas under pressure, which ispassed through the gas-permeable nest to build up a gas bed between theflat glass and the nest and is subsequently carried away again, thisobject is attained according to the invention in that the nest comprisesa plurality of spaced-apart segments, each of which has a porous and/orperforated support surface as a gas exit face, and between whichoutlet-air openings for the removal of the gas are embodied.

[0013] By means of the outflow of the gas from the planar porous and/orperforated segments of the support surface, a gas film forms between thesupport surface and the supported glass, with a pressure distributionthat is parabolic and that has no static pressure zones. Via theinterstices between the segments, the gas can readily flow out, so thatno backup of gas occurs in the middle of the glass that could causedeformation of the flat glass.

[0014] In one feature of the invention, compressed air is used as thegas. This feature allows a very simple conduct of the method by simplemeans, since suitable compressed air equipment is available on themarket.

[0015] An advantageous contactless storage and transporting of the hotflat glass is possible in a method course in which the supported glassat least intermittently has a viscosity of ≦10¹³ dpas, corresponding tothe so-called upper cooling point. For the so-called lower coolingpoint, the viscosity is ≦10^(14.5) dpas.

[0016] To obtain flat glass with predetermined properties, in onefeature of the invention a method is performed in which during thehandling of the glass, a defined rising and/or falling temperatureprofile is traversed.

[0017] Advantageously, a temperature profile is traversed by which theglass on the gas bed is ceramicized. In this way, it is possible withrelatively simple means to produce a glass ceramic plate in contactlessfashion relative to the nest, which plate does not have any punctatepits or scratches on the underside.

[0018] A favorable method course is obtained if during theceramicization, the glass is moved over the gas bed. As a result,temperature differences in the furnace can be compensated for.

[0019] In one feature of the invention, to maintain the temperaturehomogeneity required for the ceramicization, preheated gas is used.

[0020] The tempering of the gas is effected, at least predominantlyduring the flowthrough, by porous and/or perforated support segments andthus to a great extent, the temperature homogeneity required for theceramicization is achieved.

[0021] So that no contamination of the green glass to be ceramicizedwill occur, in a further feature of the invention the gas is deliveredonly via scale-free material.

[0022] An advantageous method course is obtained if the gas pressure inthe individual segments is adjusted or regulated chronologicallyvariably independently of one another. By creating a pressure gradientalong the direction of motion of the glass, for instance, a contactlessmovement of the flat glass can thus be achieved.

[0023] With the method of the invention, either a closed glass ribbon orindividual plates can be ceramicized. It is not absolutely necessary forthe underside of the glass ribbon or of the plates to be smooth. It isalso conceivable that the underside and optionally the top as well ofthe glass to be ceramicized be surface-structured, for instance studded.Also the underside in particular can be decorated.

[0024] With the provisions of the invention, a gas bed with a floatheight of between 30 μm and 1-3 mm can be created, which is sufficientfor contactless storing and transporting of flat glass. Preferably, therange is between 50 μm and 1-3 mm.

[0025] In one embodiment of the device, the device is embodied such thatthe segments extend over the entire width of the flat glass to behandled. Uniform retention of the flat glass is thus possible.

[0026] An especially simple embodiment of the device is obtained if theoutlet-air openings are embodied as slits between the segments.

[0027] A preferred embodiment of the device is obtained if theindividual segments are embodied as beams that have a box profile, intowhose interior the gas delivery is effected, and of which at least onewall, forming the support surface, is embodied as porous and/orperforated. This embodiment makes an especially simple embodiment of thesegments and outlet-air openings between the beams possible.

[0028] The beams can be realized by various kinds of molded bodies. Aparticular embodiment is obtained if the beams are formed by a boxlikeporous ceramic body. Such ceramic bodies are on the market and can bemade available for very high temperatures, as are required inceramicization.

[0029] In order to have an especially strong flow along the supportsurface, the ceramic body, with the exception of the wall forming thesupport surface, is enveloped with a gas-impermeable material. Forinstance, the ceramic body can have a suitable coating or be sheathedwith a metal foil.

[0030] The device is preferably embodied such that the segments areextended into the cold region through openings in the lateral furnacewalls, so that the connections for the compressed air can be ductedthrough to the segments without thermal stress.

[0031] An especially effective gas bed is obtained if the porous and/orperforated support surface of the segments from which the gas flows outamounts to at least 30% of the total area of the nest.

[0032] The mode of operation of the device is highly effective if aclosed gas circulation is provided, in which the gas removed through theoutlet-air openings is returned to the gas source again.

[0033] In one feature of the invention, a design of the nest that ismirror-symmetrical relative to the center face of the glass is provided,as a result of which the top and underside can be kept under exactly thesame thermal conditions.

[0034] Besides the possibility already mentioned of moving the flatglass along a pressure gradient in the segments, an onward motion of theglass can be achieved by mechanical devices that contact it, such asrollers and slides.

[0035] To avoid such mechanical devices that employ contact and thatalways require their own drive mechanism, in a further feature of theinvention the device is embodied such that the nest with the gas bed isinclined downward in the direction of motion of the flat glass. As aresult, the flat glass slides on its own to the lower location bygravity.

[0036] The invention will be described in further detail in terms of anexemplary embodiment shown in the drawings.

[0037] Shown are:

[0038]FIG. 1, in a schematic longitudinal section, a furnace chamber, inwhich a nest is set up for a flat glass pane that is retained incontactless fashion via a gas bed created by the nest;

[0039]FIG. 2, in a schematic plan view, in a first embodiment, thedesign of the nest comprising a plurality of spaced-apart individualsegments, which each have a porous and/or perforated support surface asa gas exit face, between which outlet-air openings for removing the gasare formed;

[0040]FIG. 3, in a schematic fragmentary cross-sectional view, thedesign of the individual segments by means of boxlike profiled ceramicbodies, which except for the support surface at the top have a gastightsheathing;

[0041]FIG. 4, a graph showing the pressure distribution in thelongitudinal direction of the segments; and

[0042]FIG. 5, a second embodiment with a nest segmented in beamlikeform.

[0043]FIG. 1, in a schematic view, shows a ceramicization furnace 1, inwhich a nest 2, embodied according to the invention and comprising thebeam system to be explained later, for retaining the green glass plate 3to be ceramicized is disposed by way of props 4. One prop 5 for thedelivery of a suitable gas, preferably air, is connected to the nest 2and this creates a gas bed, that is, an air cushion below the greenglass plate 3, so that there will be no troublesome mechanical contactbetween the underside of the green glass plate 3 and the nest 2. Becauseof the incline predetermined by the disposition of the props 4, thegreen glass plate 3 slides automatically in the direction of the arrowduring the ceramicization process, toward a mechanical transportingdevice, such as a roller 2 a, which feeds the green glass plateperpendicular to the plane of the paper.

[0044]FIGS. 2 and 3 show the nest 2, embodied according to theinvention, for the green glass plate 3; specifically, FIG. 2 shows thisin a plan view, and FIG. 3 in a cross-sectional view. The nest 2comprises a plurality of segments 2 ₁, 2 ₂, . . . , 2 _(n), to which thesupply 5 of gas and in particular air is connected, and which have ashomogenous an air outflow sheetwise as possible, which can be achievedby way of porous surfaces or surfaces with small perforations. Theinterstice 6 ₁, 6 ₂, . . . , 6 _(n), between these segments, which as arule is embodied as a slit, serves to remove the outlet air, which isrepresented by a downward-pointing arrow in FIG. 3.

[0045] As FIG. 2 shows, these segments and interstices extend over thefull width of the furnace, bounded by the side walls 1 a.

[0046] In the exemplary embodiment shown in FIG. 3, the air-permeablesegments are each predetermined by the upper boundary 7 a of a boxlikebeam 7, which is formed by a porous material and/or has small openings,that is, perforations. As the drawings show, these segments, that is,the upper boundaries of the beams, define relative narrow air-permeablesurfaces.

[0047] In the interior of these beams 7 ₁, 7 ₂, . . . , 7 _(n), which asgas-permeable at the top, an overpressure of a suitable gas, such asair, is created by connecting the interior of each beam to a suitablepressure source. By means of the outflow of gas from the upper box wall7 a, which is reinforced by the fact that the other walls are providedwith a gas-tight sheathing 8, a gas film develops between the top 7 a ofthe beam and the supported glass 3. When porous material is used, thepressure distribution is parabolic, as shown in FIG. 4, and has nostatic pressure zones. The gas can flow out into the interstices 6 ₁, 6₂, . . . , 6 _(n), between the beams 7 ₁, 7 ₂, . . . , 7 _(n), so thatthere is no backup of gas in the middle of the glass.

[0048] A number of advantages are attained by means of the invention.

[0049] First, a homogeneous, planar gas delivery is made possible,without creating zones of static pressure. This is advantageous, bothfor stabilizing the layer thickness of the green glass plate and formaking the temperature course homogenous. In the case of porous gas exitfaces, the gas temperature is made additionally more homogenous as aresult of the heat-exchanger effect of the porous structure.

[0050] Moreover, through the interstices between the segments, a removalof gas is assured even in the inner regions of the supported plates; asa result, arching and the development of zones of static pressure areavoided.

[0051] The preferred embodiment, with the use of beams that areperforated and/or porous at least on the top and are spaced apart,forming interstices, as segments, has the advantage of a very simpleconstruction, particularly taking into account the requisitetemperatures of up to 950° C. and higher. An essential point for this isthat porous beams, for instance of temperature-resistant ceramics, arecommercially available, and when the beams are removed from the hotregion of the furnace, as shown in FIG. 2, the rest of the constructionis exposed to only low temperatures and can be embodied correspondinglymore simply.

[0052] In FIG. 5, a second embodiment of the invention is shown, with anest 2′ of porous material that is structured in beamlike fashion. Bymeans of conduitlike structures in the nest, porous segments 2′₁, 2′₂,2′₃, 2′₄, 2′₅, . . . , 2′_(n) and outlet-air openings 6′₁, 6′₂, _(6′) 3,_(6′) 4, _(6′5), . . . , 6′_(n) are predetermined. The load-bearinginlet air, that is, the gas, flows through the segments, whileconversely the gas is carried away via the outlet-air openings.

[0053] In the exemplary embodiments, for a preferred material, theporosity is approximately 15%.

[0054] The diameter of alternative perforation openings is on the orderof 0.5 to 1 mm.

1. A method for storing and transporting hot flat glass in a contactlessmanner in glass production on a gas bed, which is constructed over agas-permeable support surface of a nest, in that a gas is passed throughthe support surface, characterized in that to attain a homogeneousdelivery of gas sheetwise, the gas is pressed through spaced-apartplanar porous and/or perforated segments of the support surface, and thegas is carried away into the interstices between the segments.
 2. Themethod of claim 1, in which compressed air is used as the gas.
 3. Themethod of claim 1 or claim 2, in which the supported glass at leastintermittently has a viscosity of ≦10¹³ dpas, corresponding to the uppercooling point, or ≦10^(14.5) dpas, corresponding to the lower coolingpoint.
 4. The method of claim 1, in which the glass, at least on itsunderside, has a surface structure, such as studs and/or a decoration.5. The method of one of claims 1-4, in which during the handling of theglass, a defined rising and/or falling temperature profile is traversed.6. The method of claim 5, in which a temperature profile is traversed bywhich the glass on the gas bed is ceramicized.
 7. The method of claim 6,in which during the ceramicization, the glass is moved over the gas bed.8. The method of claim 6 or 7, in which to maintain the temperaturehomogeneity required for the ceramicization, preheated gas is used. 9.The method of claim 8, in which the tempering of the gas is effected, atleast predominantly during the flowthrough, by porous and/or perforatedsupport segments and thus the temperature homogeneity required for theceramicization is achieved.
 10. The method of one of claims 6-9, inwhich the gas is delivered only via scale-free material.
 11. The methodof one of claims 1-10, in which the gas pressure in the individualsegments is adjusted or regulated chronologically variably independentlyof one another.
 12. The method of claim 11, in which a pressure gradientis created along the direction of motion of the glass.
 13. The method ofone of claims 1-12, in which a gas bed with a float height of between 30μm and 1-3 mm is created.
 14. A device for performing the methods of oneof claims 1-13, having a gas-permeable nest (2), disposed in a furnace(1), as a support surface for the flat glass (3) to be stored andtransported in contactless fashion, which nest has a connection (5) forthe delivery of gas under pressure, which is passed through thegas-permeable nest to build up a gas bed between the flat glass and thenest and is subsequently carried away again, characterized in that thenest (2) comprises a plurality of spaced-apart segments (2 ₁, 2 ₂, . . ., 2 _(n)), each of which has a porous and/or perforated support surface(7 a) as a gas exit face, and between which outlet-air openings (6 ₁, 6₂, . . . , 6 _(n)) for the removal of the gas are embodied.
 15. Thedevice of claim 14, characterized in that the segments extend over theentire width of the flat glass to be handled.
 16. The device of claim 14or 15, characterized in that the segments are formed by separate moldedbodies (7).
 17. The device of claim 16, characterized in that theoutlet-air openings (6 ₁, 6 ₂, . . . , 6 _(n)) are embodied as slitsbetween the spaced-apart separate segments.
 18. The device of claim 16or 17, characterized in that the individual segments (2 ₁, 2 ₂, . . . ,2 _(n)) are embodied as beams (7 ₁, 7 ₂, . . . , 7 _(n)) that have a boxprofile, into whose interior the gas delivery is effected, and of whichat least one wall (7 a), forming the support surface, is embodied asporous and/or perforated.
 19. The device of claim 18, characterized inthat the beams (7 ₁, 7 ₂, . . . , 7 _(n)) are formed by a boxlike porousceramic body.
 20. The device of claim 19, characterized in that theceramic body, with the exception of the wall (7 a) forming the supportsurface, is enveloped with a gas-impermeable material (8).
 21. Thedevice of claim 14 or 15, characterized in that the segments are formedby a beamlike segmentation of a porous molded body, in that conduitlikeoutlet-air structures are embodied in the molded body, on its top. 22.The device of one of claims 14-21, characterized in that the segmentsare extended into the cold region through openings in the lateralfurnace walls (1 a).
 23. The device of one of claims 14-22,characterized in that the porous and/or perforated support surface (7 a)of the segments from which the gas flows out amounts to at least 30% ofthe total area of the nest (2).
 24. The device of one of claims 14-23,characterized in that a closed gas circulation is provided, in which thegas removed through the outlet-air openings (6 1, 6 ₂, . . . , 6 _(n))is returned to the gas source again.
 25. The device of one of claims14-24, characterized by a design of the nest (2) that ismirror-symmetrical relative to the center face of the glass.
 26. Thedevice of one of claims 14-25, characterized in that the nest (2) isinclined obliquely downward, perpendicular to the direction of motion ofthe flat glass, and has a transport device (2 a) at the low point.